Prescott effects on motherboard power circuits

The Prescott had finally arrived, and knowing the risks I would be taking even after learning of the chip?s defeatist architecture, I went ahead and purchased the world?s first CPU built upon a 90nm process, and compatible (at least initially) with Socket-478. I?m no martyr, however; I?ve done this for you the reader. Knowing Anandtech had tested Prescott up against Northwood, and Northwood bested the 90nm chip in most benchmarks at default speeds, was ancillary to why. This question had to be answered, and furthermore was Prescott salvageable?

Intro

Motherboard power circuitry temps overclocking the Prescott 3.0E

The Prescott had finally arrived, and knowing the risks I would be taking even after learning of the chip's defeatist architecture, I went ahead and purchased the world's first CPU built upon a 90nm process, and compatible (at least initially) with Socket-478. I'm no martyr, however; I've done this for you the reader. Knowing Anandtech had tested Prescott up against Northwood, and Northwood bested the 90nm chip in most benchmarks at default speeds, was ancillary to why. This question had to be answered, and furthermore was Prescott salvageable? If not for average desktop computing, would Prescott be an Overclocker's chip? I'd read [H]ardOCP's feature forewarning of the duress Prescott's power requirement would have on motherboard's designed for an entirely different species. My curiosity, however; prevailed, and in anticipation for the 90nm silicon, I purchased the Abit AI7. First I'd like to introduce readers to one of the most comprehensive article's written concerning the engineering path leading to Prescott, Bits and Bytes by Van Smith is a must read.

Now, after extensive testing I can safely say Prescott is not entirely deserving of the reputation which preceded it. Surely the CPU could have been designed better; of course engineering hindsight is always 20/20. Irregardless of its deficiencies, the chip is in fact highly overclockable. My 3.0E SL79L easily attains a steadfast 600MHz overclock (15x 240FSB (1:1)), without any Vcore adjustment. While this doesn't compete with some Northwood's which can run 800-1000MHz beyond default, without Vcore increase, it's still very good. Another issue I can now see that has been exaggerated is Prescott's heat output. While I'm sure my temps are the result of high-quality water-block's, such as the Danger Den RBX, and Cool-Cases CF1, the average Pentium-4 cooler should still suffice for average use. Perhaps the most disconcerting issue where Prescott is concerned is not attributable to Prescott at all.

In searching for a motherboard for my new Philippine 3.0E, it never dawned on me that "Prescott Ready" entailed much more then a prima facie BIOS fix. In fact I was confident "Prescott ready" meant just that. Upon its release, I grabbed the Abit AI7 i865PE based motherboard, which features Abit's new µGuru technology. While µGuru is certainly an interesting feature, quite handy for the budding Enthusiast, it was but one small feature of the board which piqued my interest. For me the AI7 strengths lay in its BIOS, 3.30V DDR, 1.90Vcore, SATA RAID, Ethernet, 5.1sound, and the same Orb aluminium NB/HSF found on the MAX series, all these accoutrements for just $110. Ironically it was one feature included on µGuru utility monitoring GUI which became the inspiration for this article. First off, µGuru derives it's capabilities from a Winbond chip custom made for Abit, seen below;

The utility itself is quite extensive, in that it allows the end-user FSB adjustment from within Windows, harking back to the Fuzzy-Logic (Asus) and Easy-Tune (Gigabyte) moniker's. Abit took this Windows based BIOS tweaker even further, allowing control over the following voltages in addition to the FSB access; VGA, Vcore, and DDR. At this time µGuru is only Windows compatible so Linux users are out of luck. Personally I make such critical adjustments through the BIOS. I've noticed changes made via utilities similar to µGuru; often go undetected by most benchmarking software. Sandra SiSoftware, WCPUID, and others are simply unable to detect the changes. For the entry-level Overclocker, however; this isn't the end of the world. All one need do is use CPU-Z, to verify they're changes took. But I digress. What I found most interesting about AI7's µGuru, are its monitoring functions. Specifically a temp monitor labelled PWM. Pulling the reflective label off the chip we find a Winbond W83L950D monitor/controller chip;

The Winbond W83L95OD is basically a W83L784R on steroids. This chip monitor's a total of 8-voltages, 3-fan RPM's and 3-temp's including Intel's internal thermal diode. I've been around PC's now since 1987. I delved into the Enthusiast realm in 1999, and to date I've yet to see a motherboard which installed a chip able to monitor the power circuitry feeding the CPU. I've absolutely no criticism for this savvy engineering/marketing decision, and I admire the effort as much as I do seeing motherboard makers place heat-sinks on mosfetts. What occurred here is that Abit unknowingly revealed what I consider to be an unforgivable oversight. Once I dropped the Prescott into the Abit, I immediately noticed PWM temps soared whenever 3D or clock-cycle intensive programs ran. At just 200FSB and default Vcore, running Set@Home produced some sup rising results, as evidenced in the screenshot below;

Notice in the right lower hand corner of the µGuru EQ screen, PWM indicates 43C. While this may not seem excessive, it's relative to the SYS temp reading of just 12C. Next I raised the FSB to just 235FSB (1:1) pushing the 3.0E to 3525MHz. At no time did I raise Vcore at these speeds;

The PWM temps rise now to 72C after only a few minutes of running Seti@Home. In the first screenshot at default speed 43C may have been acceptable had the SYS (or ambient case temp) been lower (around 19C). Since the two screenshot's above were taken just 10-minutes apart at most, this is quite alarming. What we can extrapolate from data, is the power circuitry (PWM) becomes so hot, it actually influences the thermistor devoted to SYS temp. I found this happened again, and again. Whenever the PWM had risen excessively as a result of running LOAD even marginally overclocked, the SYS thermistor would also rise. Obviously, if the Case side-panel is removed (which it was), and we begin the benchmark where SYS = 12C, and several minutes later SYS = 20C, you can be certain the ambient temp didn't rise 8C or 15F in such a short period of time. At 72C/161F without any Vcore increase, it's obvious the power-circuitry on the Abit AI7 was not intended for Prescott.

And this is not an isolated incident. If you recall [H]ardOCP's article Overclocking the Prescott 2.8E Kyle had made the following observation/statement: "All of the motherboards we have used with Prescott's run hotter than we are used to. It is not uncommon to see components on the motherboard at 250F/120C degrees."